Manufacture and production of hard solders



Patented Feb. 6, 1940 UNITED STATES MANUFACTURE AND PRODUCTION OF HARD SOLDERS Alan Richard Powell, London, England, assig'nor to Johnson, Matthey & Company, Limited, London County, England, a company of Great Britain No Drawing. Application October 27, 1938, Serial 'No. 237,368. In Great Britain December 20,

4 Claims.

This invention relates to the manufacture and production of hard brazing solders, in particular silver solders, in the form of fine metallic powders.

5 Such solders usually consist of a combination of copper and/or silver and/or gold with zinc and/or cadmium and/or tin and/or phosphorus, generally speaking of two or more of the metals gold, silver and copper on the one hand and one 10- or more of the elements zinc, cadmium, tin and phosphorus on the other hand. For precious metal, work, platinum and/or palladium may also be employed.

These solders are usually sumciently malleable l5 and ductile to allow of their being workedeither hot or cold into sheet or rod or wire, but in all cases the malleability is sufficient to prevent their being converted into powders by mechanical grinding processes. They may be commi- 20 nuted to a certain extent, however, by sawing, rasping, filing or milling operations; these are tedious and costly and yield relatively coarse powders which cannot be introduced into very fine interstices. g According to this invention solders of the said kind are obtained in the form of fine powders by dividing the components of the desired solder alloy into two portions, the first comprising components which are such as to form a brittle or 30 readily pulverized alloy, the second comprising a single malleable metal or mixtures of metals which are such as to form a malleable alloy, alloying the components of the first portion and reducing the resulting alloy to powder form by suitable mechanical means, such as grinding, producing the component or components of the second portion in the form of a fine powder by suitable means, as for example by subjecting a compound of the component or components to a conversion operation while intimately mixed with a distributing agent capable of being removed without detriment to the component and removing the distributing agent. For example, to prepare a fine silver powder a mixture of silver nitrate and calcium or magnesium nitrate (corresponding to a ratio by weight of Ag:Ca or MgO=-l:1) is dissolved to give a 10 per cent aqueous solution andthe solution poured into an amount of a boiling solution of sodium carbonate or caustic soda more than sufilcient to precipitate the corresponding carbonates or hydroxides. The resulting precipitate is washed with hot water to remove soluble salts, and dried. The resulting mixture is then subjected to a dis- 55 sociation or reduction treatment as follows. For

the purposes of dissociation, the mixture is heated in air at a temperature of from 300 to 900 centigrade. Higher temperatures maybe used but in this case the silver melts and forms minute spheres. The reduction treatment may be car ried out by heating the mixture, for example in an atmosphere of hydrogen, at a temperature of: from 200 to 900 centigrade. The product of either the dissociation or reduction treatment is a finely divided silver powder homogeneously dispersed throughout the distributing agent, i. e., calcium or magnesium carbonate or oxide. The distributing agent is then separated, for example by leaching with a suitable dilute acid, such as aceticacid.

The resulting silver powder, especially when the lower temperatures mentioned are used, is extremely fine and will remain in suspension in water for an appreciable time, and shows no tendency to cake together when it is washed and dried.

For the production of an alloy of silver and copper in the finely powdered form a mixture of silver and copper nitrates in such a proportion as to-give the desired copper-silver ratio in the alloy, is dissolved in water to give a 10 per cent solution, which is mixed with an equal volume of a 10 per cent aqueoussolution of calcium ,ormagnesiumnitrate, and the mixed solution is poured into an amount of a boiling solution of sodium carbonate or caustic soda more than sufiicient to precipitate the corresponding carbonates or hydroxides. The resulting precipitate is washed with hot water, dried and subjected to a reduction treatment at a temperature of from 300- 900 centigrade, in an atmosphere of a reducing gas, as for, example hydrogen, water gas, or producer gas, whereby all the copper and silver compounds are reduced to the corresponding metals. In this way a silver-copper alloy is obtained in the finely powdered form, intimately mixed with calcium or magnesium oxides. The distributing agent is then removed, for example by leaching with a suitable dilute acid such as acetic acid or sulphuric acid.

The above examples of the process 01 forming the fine powders illustrate the process described in the co-pending application Serial No. 237,320, filed October 27, 1938. The fine powders of the two portions of the solder are then intimately mixed.

For example if it is desired to prepare an alloy of parts of silver, 15.5 parts of copper, 16.5 parts of zinc and 18 parts of cadmium in the der is produced bythe method described in Example 1 of the co-pending application Serial No. 237,320 filed October 27, 1938; During the grinding operation the fine particles of silver, which are relatively soft, become distributed-over the.

surface of the relatively hard particles of the brittle alloy thus producing a very intimate mixs it ture of the components of the final solder alloy.

The wet powder is washed out from the mill and a small amount-of acid maybe added to the suspension to produce flocculation of the alloy I particles. Certain impurities introduced during grinding remain suspended in the water after the.

alloy has settled and may then readily be Washed away by elutriation. The flocculent powdered alby is then washed free from acid and dried;

during the dryingoperation, the product again falls to a fine powder. This powder may be used with great advantage for soldering especially when itis desired to introduce the solder into fine apertures and into places which would be inaccessible to solders in the ordinary form, such as sticks. The actual soldering operation can be carried out in bright annealing furnaces of any type so that by the use of these solders, soldering operations may be carried out on mass production principle.

If desired suitable fiuxes may be mixed with the powders to assist in rapid wetting of the parts to be soldered.

Other malleable alloys may be prepared by dividing the components into two portions and adopting a procedure similar to that described above.

The following examples will further illustrate how the said invention may be carried out in practice, but the invention is not restricted to these examples.

Example 1 For the preparation in powder form of a solder alloy comprising 43 parts oi' silver, 37 parts of copper and 20 partsv of zinc.

A brittle alloy is prepared by melting together 16 parts of copper and 20 parts of zinc. The molten alloy is poured into water and the resulting granules converted into a coarse powder by stamping. This coarse powder is then ground with water in a ball mill until it passes through a ZOO-mesh screen.

A malleable alloy of 43 parts of silver and 21 parts of copper is prepared in powder form by the method described in the co-pending application Serial No. 237,320, filed October 27th, 1938, v

the resulting powder then being added to the ball mill containing the powdered brittle alloy.

Grinding is continued for, about /2 to 1 hour. The

product is washed out from the mill with water and the resulting suspension coagulated by the addition of sulphuric acid to produce a solu-- tion of about 0.5 per cent strength. The coagulated powder is washed by elutriation with 0.5 per cent sulphuric acid to remove impurities introduced by the grinding, and then with water During the course of the- Example 2 Forjthe preparation inpowder form of an alloy comprisingequal parts of silver, copper and zinc,

the brittle alloy is prepared as described in Example 1- from the copper and thenzinc and, after grinding,' -the silver is' added in the form of a fine powder obtained by a suitable method.

. Example 3 For the preparation in powder form of a solder alloy containing 20 parts of tin. 56 parts of silver and 24 partsof copper, the brittle alloy is prepared trom 20 parts of tin, 24 parts otscopper and 16 parts of silver inthe manner described in Ex- 7 ample 1. To' the resulting product there are addedthe remaining 40 parts oi silver in the form '01 afine powder prepared for example according to the oo-pending application Serial No. 237,320, filed October 27th, 1938.

Example}.

For the preparation in powder form of a solder alloy containing parts or copper, ,15 parts 'of silver and 5 parts of phosphorus, the brittle alloy consists of 50 parts of ordinary commercial 10 percent phosphor-copper and the malleable powder alloy consists of 35 parts of copper and 15 parts or silver. l I Example 5 For the preparation in powder form of a solder alloy containing 37.5 parts 01' gold, 20 parts of cadmium, 3 parts of zinc, 21.5 parts of silver and 18 parts of copper, the brittle alloy consists of 20 parts of cadmium, 3 parts of zinc, 18 parts of copper and 7 parts of silver, while the malleable alloy consists of 37.5 parts of gold and 14.5 parts 01' silver.-

What I claim is: r

1. A process of producing in the form of fine metallic powders hard solders which cannot be comminuted by a simple pulverizing process which consists in dividing the components or the desired solder alloy into two portions, the first comprising components which are such as to form an alloy capable of being readily pulverized, and the second comprising a relatively workable material'selected from the group malleable metals, malleable alloys, alloying the components of the first portionand reducing the resulting alloy to powder iorm by'a pulverizing'process, producing thematerial of the second portion in the form of a fine metallic powder by converting a powdered oxide material into metal while mixed with a distributing agent and then removing the distributing agent, and finally intimately mixing the two portions.

2. A process of producing in the form of fine metallic powders hard solders which cannot be comminuted by a simple pulverizing process which consists in dividing the components of the desired solder alloy into two portions, the first comprising components which are such as to form an alloy capable of being readily pulverized,

and the second comprising a single workable metal, alloying the components of the first portion and reducing the resulting alloy to powder form by a pulverizing process, producing the material of the second portion in the form of a fine ,metallic powder by converting a powdered oxide of the metal into metalwhile mixed with a distributing agent and then removing the distributing agent, and finally intimately mixing the two portions.

3. A process of producing in the form of fine metallic powders hard solders which cannot be comminuted bya simple pulverizing process which consists in dividing the components of the desired solder alloy into two portions, the first comprising components which are such as to form an alloy capable of being readily pulverized, and the second comprising components which are such as to form a workable alloy, alloying the components of the first portion and reducing the resulting alloy to powder form by a. pulverizing' process, producing the material of the second portion in the form of a fine metallic powder by converting a powdered oxide thereof into metal while mixed with a distributing agent and then removing the distributing agent, and finally intimately mixing the two portions.

4. A process according to claim 1 in which the final reduction of the first portion to a flnepowder and the mixing of the two portions arecarried out wet in a mill, the wet powder is washed from the mill with water, the resulting suspension is coagulated with dilute sulphuric acid, impurities are washed awaynby elutriation, the powder is washed free from acid and then dried.

' ALAN RICHARD POWELL. 

